Wont to remove trim an tilt unit from motor ,( unit leaks down ) do i need to take motor off boat or can it be left on ? 1986 175 2.4L

If you support the motor while it is tilted up (rope, engine hoist, floor jack) you can pull off the Starboard engine bracket and leave the Port side bolted to the transom.
BE CAREFUL!! the motor can slide off of the tilt tube while the Starboard plate is off!

thanks for the info , i read in the manual about putting a block of wood and a c clamp ? but could not see the picture very well, to see where to put it. thanks again

The 2X4 fits in different places from boat to boat. You will see wher it fits for you when you get it apart. Mainly you need to prevent the motor from sliding off of the tilt tube.. I usually just put the nut back on after the side clamp bracket is off. And if the trim is going to be off for a while, put the clamp bracket back on and you are good.